1. Field of the Invention
The present invention generally relates to a method and apparatus for applying a particulate material to a substrate and, more particularly, to a fluidized bed apparatus and method of using such apparatus for applying a particulate material to a substrate.
2. Background of the Related Art
Application of materials to a substrate is commonly performed in order to manipulate various mechanical, chemical, physio-chemical, and/or electronic properties of the substrate. Particulate materials such as powders and fibers represent forms of material that may be applied to a substrate in order to modify the properties thereof. For example, metal substrates may be coated with powdered organic resins. Upon application of sufficiently high temperatures, the resinous particles melt and fuse on the surface of the metal substrate to form a continuous coating that enhances the chemical resistance of the metal substrate.
Particulate materials may also be applied to fibrous substrates, such as aggregations of non-woven and synthetic fibers. The particulate may thereby become enmeshed within the fibrous aggregate. Substrates treated in this way may be used to form absorbent articles including feminine hygiene articles such as sanitary napkins, tampons, and panty liners, as well as diapers and incontinence articles. During the manufacture of such articles, a fluid-absorbing powder (e.g. a superabsorbent powder) is applied to a moving fibrous substrate. The superabsorbent powder is thereby transferred to the surface of the fibrous material or regions within the fibrous material, thus enhancing the absorbent properties of the fibrous substrate.
The application of particulate materials to a substrate may be accomplished by any one of a number of know conventional means. For example, particulates may be applied using mechanical delivery devices such as conduits, nozzle sprayers, and the like.
Unfortunately, using conduits, nozzles, and the like to deliver particulate material to a substrate, particularly a substrate moving at a high speed, is subject to variety of problems. For example, it is difficult to apply the particulate material to a pre-determined, localized area of the substrate. In particular, if the spraying of the powder is not initiated and terminated within a tightly defined time interval, the particulate may be delivered to undesired locations rather than the desired location on the substrate. Furthermore, the particulate material is often subject to spreading, i.e., the particulate does not remain localized on the substrate and the particulate may migrate to locations where it is not desired, thereby contaminating the process. The above problems are compounded for substrates, including fibrous substrates, which are often processed at line speeds that are fast enough to promote scattering of the particulate to undesired locations on the substrate. Therefore, a need exists for a method and apparatus for applying a particulate material to a substrate that overcomes one or more of the above-mentioned drawbacks.